1. Field of the Invention
The present invention relates to a toner and a developer using the toner, and more particularly to a toner and a developer using the toner for use in electrostatic copying processes in image forming apparatuses such as copiers, facsimiles and printers.
2. Discussion of the Background
A developer used in electrophotography, electrostatic recoding or electrostatic printing is attached to an image bearer such as a photoreceptor an electrostatic latent image is formed on in the developing process, transferred to a transfer medium such as a transfer paper from the image bearer in the transfer process and fixed on the transfer paper in the fixing process.
A magnetic brush method, a cascade developing method or a powder cloud method is known as a method of visualizing an electrostatic latent image with a toner.
Typically, after an electrostatic latent image is developed on a photoreceptor with a toner to form a visible toner image thereon, the toner image is transferred onto a transfer sheet and fixed thereon. A toner image is typically fixed thereon by a heat-roll fixing method pressing the toner image upon application of heat onto a transfer sheet. Although the heat-roll fixing method is capable of quickly fixing a toner image because of its high heat efficiency, so-called an offset problem that a part of a toner image adheres to the surface of the roll, remains thereon and transfers again onto a transfer sheet tends to occur.
Conventionally, the surface of a fixing roller is formed of a material having good releasability from a toner, such as a silicone rubber and a fluorine-containing resin, to prevent the offset problem, and further a liquid having high releasability, such as a silicone oil and a fluorine-containing oil, is applied to the surface thereof, to prevent the offset problem and the fatigue of the surface thereof.
Although this prevents the offset problem very effectively, an applicator applying a liquid preventing offset problem is needed in a fixer, resulting in a problem that the fixer has a complicated configuration. In addition, the oil application causes peeling of layers forming the surface of a fixing roller, resulting in a shorter life thereof.
Published Unexamined Japanese Patent Applications Nos. 60-230663 and 1-234858 disclose a method of adding a release agent such as low-molecular-weight polyethylene and low-molecular-weight polypropylene in a toner in consideration of applying a liquid preventing offset problem from the toner when fixed upon application of heat and pressure instead of using the oil applicator.
A toner is conventionally prepared by uniformly mixing toner constituents such as a binder resin and a colorant in the shape of a powder, fusing and kneading the toner constituents, cooling the kneaded toner constituents to be hardened, pulverizing the hardened toner constituents, and classifying the pulverized toner constituents.
Recently, the toner is more required to have a smaller particle diameter in terms of producing higher quality images.
When an airflow pulverizer pulverizes a toner to have a smaller particle diameter, the resultant toner has a larger specific surface area and lower fluidity.
In addition, a toner is prepared by a polymerization method as well besides the above-mentioned method.
A toner prepared by the polymerization method has a smaller particle diameter and easily produces high definition images. In addition, the toner is spherical, and has a small specific surface area and constant fluidity. Further, the toner has good transferability to a receiving material.
However, the polymerization method has high production cost because of incapable of recycling an off-specification toner such as a fine powder produced during the process of preparing the toner. In addition, almost all the toners are spherical and easily scrape through cleaning members such as a cleaning blade in the process of cleaning a photoreceptor, resulting in poor cleaning.
Therefore, the above-mentioned fusing, kneading and pulverizing method is still used as a mainstream method as the polymerization method is.
Published Unexamined Japanese Patent Application No. 2005-215148 discloses a toner and a method of preparing the toner as a method of downsizing the particle diameter thereof, which is prepared by the fusing, kneading and pulverizing method, wherein the toner includes at least a binder resin and a colorant, prepared by the fusing, kneading and pulverizing method, has a volume-average particle diameter of from 5.0 to 8.5 μm, and has a circularity of form 0.955 to 0.980.
Namely, Published Unexamined Japanese Patent Application No. 2005-215148 discloses a method of preparing a toner having a small particle diameter, a high circularity, good transferability and producing quality images, which is prepared by a method including at least a process of pulverizing with an impact pulverizer.
However, when a toner prepared by the method disclosed in Published Unexamined Japanese Patent Application No. 2005-215148 includes a release agent, the probability of being exposed thereof on the surface of the toner increases.
When the release agent exposed on the surface of the toner increases, it leaves therefrom and adheres to a carrier when the toner is used therewith as a two-component developer and other charging members, resulting in deterioration of the chargeability and durability of the developer. Further, the release agent is also known to deteriorate the fluidity and transferability of a toner to a paper.
Therefore, when a toner has a smaller particle diameter, a wax therein preferably has a smaller dispersion diameter as well.
Published Unexamined Japanese Patent Application No. 3-168649 specifies that a low-molecular-weight wax in a binder resin has a dispersion diameter not greater than 1 μm. An object thereof is to prevent the offset problem, and a method of kneading toner constituents for a long time with a large shearing force is disclosed therein such that the wax has a desired dispersion diameter.
However, Published Unexamined Japanese Patent Application No. 3-168649 has low productivity because the production equipment having a large shearing force is limited and the toner constituents are kneaded for a long time.
Published Unexamined Japanese Patent Application No. 11-190914 discloses a toner for full-color electrophotography, wherein a colorant has a dispersion diameter not greater than 1 μm and release agent has a dispersion diameter of form 0.1 to 2 μm in a binder resin, and the following relationship is satisfied:Q20/Q600×100=70% or more (Z %: charge buildability)wherein Q600 is a charge quantity of the resultant developer when the toner is mixed with a carrier at a concentration of 5% while stirred for 10 min at normal temperature and humidity; and Q20 is a charge quantity of the resultant developer when the toner is mixed with a carrier at a concentration of 5% while stirred for 20 sec at normal temperature and humidity.
Namely, Published Unexamined Japanese Patent Application No. 11-190914 discloses a masterbatch wherein a release agent as well aw a colorant are more uniformly dispersed in a binder resin.
However, Published Unexamined Japanese Patent Applications Nos. 3-168649 and 11-190914 do not downsize both of the average particle diameter of a toner and the average dispersion diameter of a release agent. When a release agent is not uniformly dispersed in a toner, the release agent exposed on the surface thereof increases, resulting in deterioration of fluidity and durability of the toner.
Because of these reasons, a need exists for a toner having good fluidity and durability as well as a small particle diameter.